This invention is concerned with the problem of drill steel stability during drilling operations, i.e, earth drilling operations.
In deep hole drilling operations, it is necessary to effectively engage the drill string at the ground surface. Such drill string engagement must be firm enough to provide desired drill string stability, yet allow movement of the drill string downward under rotary thrust load. A common expedient used is the provision of a bushing which is slightly oversize in relation to the outside diameter of the drill rod used in the drill string. After a short period of time, the drill cuttings coming from the hole being drilled, abrade the bushing and cause it to wear out, i.e., the inner diameter of the bushing is enlarged. As a result, the clearance between the bushing and drill rod will allow loose engagement of the bushing with the drill rod, causing the latter to become unstabilized resulting in drill rod whip with attendant damaging vibrations.
A prime object of this invention is to provide a drill rod table bushing arrangement which avoids drill rod whip during drilling operations.
A more specific object is to provide a drill rod table having a bushing arrangement which maintains a stabilizing grip on the drill rod even after prolonged use under high rotary thrust loading.
Another object is to provide a drill rod table having a bushing arrangement which has pneumatic pressure means to develop a stabilizing action on the drill rod being gripped thereby.
Still another object is to provide flow of pressurized fluid to restrict flow of drill cuttings upwardly into the bushing surrounding the drill rod .